ABSTRACT Periodontal diseases are caused by host inflammatory responses to dysbiotic oral microbiota resulting in the progressive destruction of supporting hard and soft tissues of the peridontium. It is estimated that approximately 50% of the US population will suffer from some form of periodontal disease. Neutrophils are the most common anti-microbial effector myeloid cells recruited to the oral cavity under both physiological and pathological conditions. Although neutrophils are associated with the initiation and progression of periodontal diseases, we know little about the specific immune pathways that drive neutrophil recruitment or activation at the gingival barrier. The NADPH oxidase enzyme complex is highly expressed in neutrophils. On activation, the NADPH oxidase generates superoxide which is enzymatically or spontaneously converted to reactive oxygen species (ROS) that have antimicrobial and immuno-regulatory functions. Our preliminary data demonstrates a key role for NADPH oxidase derived-ROS in limiting neutrophilic effector functions in response to periodontal pathogens. Oxidase null neutrophils generated excessive amounts of inflammatory mediators in response to oral bacteria. Oxidase deficiency in mice resulted in profound inflammation characterized by excessive mobilization and tissue accrual of neutrophils. These data support a somewhat counterintuitive role for ROS in limiting host inflammation. Our central hypothesis is that the NADPH oxidase derived-ROS, independent of their antimicrobial functions, play key roles in redox modulation of neutrophil effector functions in vitro and in vivo. Further, we hypothesize that while excessive amounts of ROS are associated with the pathophysiology of periodontal diseases, low-level, localized ROS responses are immuno-regulatory. These hypotheses will be tested in two specific aims. 1) We will determine the specific intracellular signaling pathways modulated by oxidants that limit neutrophil degranulation and transcriptional responses to oral bacteria. 2) We will also investigate the role of sentinel macrophages and ROS from microbial sources in modulating neutrophilic inflammation in vivo. The use of conditional knockout mice that specifically lack NADPH oxidase activity in neutrophils will enable us to specifically determine the role of oxidants in regulation of neutrophil effector functions in a cell intrinsic manner in vivo. The data generated by these studies will not only shed key mechanistic insights in neutrophil biology, but also enhance our understanding of immune pathways relevant in gingival inflammation and their regulation by oxidants. Further our studies are also highly relevant in understanding the immunopathology of chronic granulomatous disease, a life-threatening pediatric immuno-deficiency caused by inherited mutations in NADPH oxidase genes.